1. Field of the Invention
The invention relates to a polarized electromagnet comprising:
a coil adapted to be fed with DC current, PA1 a magnetizable core which is movable between two longitudinal end positions occupied alternately by sliding inside the carcase of this coil, and which has two opposite external widened pole portions extending transversely with respect to the axis of the coil, PA1 a fixed yoke having axially, on each side of each widened pole portion, a pair of pole extensions having opposite magnetic polarities which are conferred thereon by permanent magnetic means placed therebetween and orientated so that their magnetic axes are parallel to said axis, said widened pole portions cooperating with said extensions so that, for each of the two end positions, the magnetic flux sent by said magnetic means through the core is of opposite direction.
2. Description of the Prior Art
Such electromagnets have a great interest for actuating relay or contactor switches where a good sensitivity and/or current economy are desirable.
An electromagnet having the above defined structure is known for example from French Patent No. 1 603 300 where it is applied to a polarized relay used for switching small currents.
In such a polarized relay, the use of a permanent magnet of annular shape and that of a cylindrical core, with the ends of which are concentrically associated two parallel disks, provides a symmetry of the magnetic attractions and repulsions which reacts at the same time on the sliding of the core inside the coil; such a relay has however the drawback of requiring the use of two permanent magnets for magnetizing the three separate pieces forming therewith the fixed yoke of the relay. In addition, the lateral and totally offcentered location of the magnets which gives to the assembly a flat shape of small thickness, defines proportions which it is difficult to use in some applications. In this known relay, the use of the two magnets and of the three pieces was made necessary because these pieces play a secondary role which is that of participating with the core in forming a switch for low current; for this, the permanent magnets require insulating ceramics for forming a galvanic insulation between the three pieces.
The invention proposes making improvements to this known relay for simplifying its structure when the core is associated directly or indirectly with a separate switch requiring, for switching thereof, the use of a higher force, while keeping the advantages from which it may benefit relatively to the generation of pulling forces perfectly concentric with the coil.